The Effect of Boiling on the Mass Transfer of Corrosion Products in High Temperature, High Pressure Water Circuits

The behavior of haematite was studied in a boiling water loop operating at pressures up to 5.7 MPa. Nucleate boiling, induced at different temperatures and pressures, increased the deposition of haematite on heated surfaces, with both deposition and boiling increasing downstream of the onset of boiling. Deposition rate constants at boiling surfaces ranged from 7 to 200 μm s⁻¹ and averaged 60 μm s⁻¹, and on nonboiling surfaces they ranged from 4 to 50 μm s⁻¹ and averaged 15 μm s⁻¹. Release rates of corrosion products (crud) from isothermal surfaces were calculated in the range 0.3 to 3 μg m⁻² s⁻¹. The behavior of crud deposits during cleaning provided further evidence of the consolidation of deposits with time, temperature and, possibly, bulk boiling.